1. Field of the Invention
This invention relates generally to hybrid gas turbine engine rotors having ceramic and alloy metal portions and, more particularly, to a new and improved connection between the ceramic and the alloy metal portions.
2. Description of the Prior Art
Gas turbine engines have been proposed utilizing ceramic hot section components which withstand higher temperatures than corresponding alloy metal components and, therefore, offer the possibility of increased cycle temperatures and improved engine efficiency. However, because ceramic is a material not well suited to all engine operating environments, hybrid rotors have been proposed including ceramic turbine wheel portions for maximum temperature operation and alloy metal shaft portions for maximum structural integrity and durability. Because ceramic has a lower coefficient of thermal expansion than alloy metal, each of these proposals has necessarily addressed the problem of connecting the ceramic and alloy metal portions through an arrangement which transfers torque and accommodates relative thermal growth. In one proposal, the connecting arrangement includes a solid ceramic stub shaft of non-circular cross section on the turbine wheel portion received in a correspondingly shaped socket in the alloy metal shaft portion for torque transfer with resilient means between the socket and the ceramic stub shaft to accommodate relative thermal growth. In other proposals, various clamping arrangements are provided to clamp the ceramic and metal components together with resilient means provided therebetween for accommodating relative thermal growth. In still another proposal, an alloy metal shaft is brazed to a hollow ceramic stub shaft integral with the ceramic wheel portion. And in yet another proposal, the ceramic turbine wheel portion has a metal connector attached to it by a so-called "thermal insertion" technique, the metal connector having face splines for engagement with corresponding face splines on the alloy metal shaft portion and the entire assembly being axially bolted. These various ceramic-to-metal connecting arrangements are less than ideal because of uneconomical complexity and/or because they are not well suited to heat flow management through the rotor. A hybrid turbine rotor according to this invention includes a new and improved connection between a ceramic turbine wheel portion and an alloy metal shaft portion which is simple, efficient and particularly adapted for heat flow management.